Locating a target region in a body, for example an anatomical cavity in a body of a patient, is important, inter alia, for anaesthetics, or biopsy or aspiration of material from the cavity.
For example, a regional anesthesia block of the epidural tissue-space is understood to produce effective transient anesthesia of the lower extremities of the body. It can be effectively used for a vast number of invasive procedures of the body, including but not limited to, child birth, prosthetic hip replacement, and a variety of other surgical procedures where anesthesia below the waist is required. It can also be effectively used for treatment of chronic and acute pain including, for example, “back-pain,” ailments of the vertebrae and, compression of the accessory nerves of the spinal column. To achieve effective regional anesthesia and to block nerve transmission to the Central Nervous System an adequate volume of a local anesthetic solution must be deposited in close proximity to the spinal cord at a particular level of the vertebral column within the anatomic site known as the epidural “space.”
The epidural space is that part of the vertebral canal not occupied by the dura mater and its contents. It lies between the dura and the periosteum lining the inside of the vertebral canal. It extends from the foramen magnum to the sacral hiatus. The anterior and posterior nerve roots in their dural membrane pass across the epidural space to unite in the intervertebral bodies, and the intravertebral discs. Laterally, the epidural space is bordered by the periosteum of the vertebral pedicles, and the intervertebral foramina. Posteriorly, the bordering structures are the periosteum of the anterior surface of the laminae, the articular processes and their connecting ligaments, the periosteum of the root of the spines, and the interlaminar spaces filled by the ligamentum flavum. The space contains venous plexuses and fatty tissue which is continuous with the fat in the paravertebral space.
The epidural fluid filled space (posterior epidural space) is a limited anatomic area with an irregular shape measuring in several square millimeters with respect to the cross section of the vertebrae and spinal column. The fluid filled space is very narrow and is associated closely with the dura of the spinal column with the ligamentum flavum closely adjacent. The fluid filled space therefore has to be clearly identified when the bevel or point of the needle exits the ligamentum flavum, as the dura will be punctured if the needle continues to penetrate. The standard technique for locating the epidural fluid filled space employs the “loss-of-resistance” (LOR) technique. This technique utilizes a low-friction syringe made of plastic or glass connected to an epidural Touhy needle (16 to 18 gauge). In addition, other pump driven systems have been developed to identify the epidural space by utilizing pressure monitoring with visual and acoustical representation of the fluid pressure within the system or at the tip of the needle.
When performed, the technique has the patient either in the sitting or lateral decubitus position. The patient should be encouraged to adapt a curled up position, as this tends to open the spaces between the spinous processes and facilitates the identification of the intervertebral spaces. Epidural injections can be sited at any level along the lumbar and thoracic spine, enabling its use in procedures ranging from thoracic surgery to lower limb procedures. Patients may also be placed lying face-down to expose the dorsum of the back when performing this procedure in conjunction with fluoroscopy.
The clinician palpates the vertebral column at the appropriate level of the vertebral column between vertebrae. Local anaesthesia is placed within the superficial tissues rendering the tissues of the area to be locally anesthetized. The dermis is then punctured using the Touhy needle and the needle is advanced while the clinician simultaneously applies pressure on the plunger of the syringe.
Insertion of the epidural needle continues and advances through the supraspinous ligament, with the needle pointing in a slightly cephalad direction. The needle is advanced into the interspinous ligament, which is encountered at a depth of 2-3 cm, until the subjective sensation of increased resistance is felt as the needle passes into the ligamentum flavum.
When using a LOR syringe the needle is advanced until the subjective “feel” of resistance by the clinician results in a distinct “back-pressure” on the plunger. The clinician must subjectively differentiate the “back-pressure” or resistance encountered to identify the location of the anatomic structure of the ligamentum flavum. The epidural fluid filled space is entered by the tip of the needle after it passes through the ligamentum flavum thus identifying a True-LOR
During the advancement of the needle within the tissues it is common for the operator to identify a drop of pressure or a false-LOR. The false-LOR can be attributed to the needle tip entering into a low density tissue structure such as a vacuole (adipose tissue) or an anatomic structure with a high tissue compliance such as the interspinous tissues. Repositioning of the needle (forward and backward) occurs many times as a needle makes contact to bony vertebrae as one is attempting to find the correct trajectory to the epidural space. Any backward movement (retraction) of the needle along a path during the repositioning creates a drop in pressure in the fluid, which can result in a false-LOR further complicating the detection of a true-LOR.
The movement of the Touhy needle from penetration of the dermis to identification of the ligamentum flavum can vary from greatly in depth depending on the patient's physical size. The needle must travel along a distance through the tissues. Needle movements can create a False-LOR as previously described and this is magnified in those patients that are larger in size. Overweight patients also present a greater challenge, and with the morbidly obese patient the epidural injection may not be suitable because of the limitations of subjective nature of this technique. The morbidly obese patient has increased adipose tissue distributed throughout the body and those patients with increased adipose content present a greater challenge because of the distribution of vacuoles within these various tissue planes. Age appears to be an additional complicating factor because of the challenge presented by the reduced size of the anatomy of the epidural tissue-space and stenosis of the vertebrae such that needle tip contact to the bony surface often requires re-alignment and retraction of the needle to find the correct trajectory. Also, in small children tissue compliance is difficult to discriminate and False-LOR's are found making the procedure more dangerous.
False-LORs can lead to many problems. For example, excess fluids can be indiscriminately injected while trying to determine the location of the epidural space. The additional fluid released into these tissues can further complicate the identification of epidural space. Additionally, if the doctor has difficulty discriminating between a False-LOR and a True-LOR, the Touhy needle may be moved beyond the boundary of the epidural space and inadvertently advanced into and through the dura of the spinal cord producing what is termed a “wet-tap”, which can have a dangerous long-term consequences to the patient.
Therefore, discriminating between a False-LOR and True-LOR for the practitioner is important when performing an epidural injection as this technique carries the risk of direct spinal cord injury resulting in transient or permanent nerve damage and even unintended death to the patient.
Ucha Calvo EPO 0538259A1 describes a method and apparatus for locating anatomical cavities such as the epidural space. The identification of the epidural space is based on a loss of resistance with a syringe by the emission of acoustic and visual warning signals which quantify and corroborate the tactile feelings of the operator. The method is independent of the pressure characteristics of the space to be detected. Ucha describes a first warning signal with pre-determined frequency and amplitude, which stops if the pressure returns to a constant recovery to the present value when the plunger is manually depressed, and a second warning signal with a different warning from the previous one used in both frequency and amplitude, in response to a drop in pressure in which the pressure cannot be recovered through manually depressing the plunger.
Thus Ucha describes two conditions, both initially represented by a sudden drop of pressure (i.e., a loss-of-resistance), which are then differentiated by one state in which a pressure can revert back to a pre-established level and a second state in which pressure cannot revert back to the pre-established pressure value. This system has the drawback that the differentiation between false-LOR and true-LOR is dependent upon the pressure placed upon the plunger by the user, and is thus subject to operator bias.
U.S. Pat. No. 6,200,289 (also published as WO/1999/52575) to Hochman et al. (incorporated herein by reference) discloses an automatic injection device that includes a drive mechanism that causes a therapeutic fluid to flow from a cartridge supported by a cartridge holder, a tube and a handle with an injection needle. The drive mechanism is connected to an electric motor and a sensor positioned at the motor output that measures the force applied by the motor to the drive mechanism. This force is then used to determine an internal characteristic such as a force or internal pressure generated during the injection process. This characteristic is then used as a control parameter by a microprocessor or controller which generates corresponding commands to the drive mechanism. In a particularly advantageous embodiment, the characteristic is used to calculate an exit pressure at which fluid is ejected by the device through an elongated tube. The electric motor is then operated in such a manner that the exit pressure is maintained at a predetermined level to insure that a patient does not suffer pain and/or tissue damage. Additionally WO/1999/52575 teaches the use of visual and constant current aural information, for example to feedback information about system pressures to the user. Although such information can assist clinicians in performing epidural injections, the problem of false LOR is not specifically addressed.
U.S. Pat. No. 7,922,689 (also published as WO/2003/000146) to Lechner discloses a device for locating an anatomic cavity that relies on an acoustic sound signal that is continuously representative of the pressure prevailing in the fluid (i.e. audible or visual warning signal). However this system has no capacity to discriminate between a drop in pressure related to a false-LOR versus a true-LOR, as this system only provides continuous acoustic feedback that does not distinguish between these two conditions.
Published U.S. patent application US2006/0122555 (also published as WO/2007/024399) to Hochman, describes an automatic injection device which includes a drive mechanism and a sensor used to determine an internal characteristic such as a force or internal pressure generated during an injection process. The entire disclosure of both U.S. Published Application No. 2006/0122555 and PCT Publication No. WO/2007/024399 are incorporated herein by reference. The internal characteristic is then used as a control parameter by a microprocessor or controller to determine the exit pressure of the fluid expelled by the device. This exit pressure is then used to identify the kind of tissue in which the injection is being introduced. This publication discusses how false-LOR can be identified when using the computer controlled drug delivery system with exit pressure control. Once the needle enters such a space the pump is turned on thereby quickly filling the space (or pressurizing the less dense tissue with fluid) such that the recorded exit pressure would once rise and objectively indicate a false-LOR.
Published patent application US2014/0012226 (also published as WO/2014/007949) to Hochman, the entire disclosure of which is incorporated herein by reference, describes an automatic injection apparatus which uses non-continuous fluid-flow of drugs to identify an intended injection site and includes a drive mechanism, a sensor and a controller for establishing fluid flow and pressure and preventing fluid flow until the pressure drops below a predetermined threshold. The pressure threshold is determined based on an internal pressure generated during an injection and more fluid will not flow until it drops below a predetermined pressure. An injection is performed to establish an initial pressure threshold and then to stop the fluid flow into a patient until the pressure drops below a predetermined pressure which allows fluid flow to resume, thus identifying a fluid filled tissue space. The initial pressure threshold is used as a control parameter for a microprocessor which controls the rate of injection. Fluid flows below certain pressures are also used to identify a specific location within the body during injections. Again false-LOR is identified by filling the space (or pressurizing the less dense tissue with fluid) such that the recorded exit pressure would once rise and objectively indicate a false-LOR.
U.S. Pat. No. 8,608,665 to Vad describes a device for pressure detection which may be used in conjunction with a syringe and needle. The device is described as including a pressure transducer, a microprocessor and a light emitting diode. The pressure transducer is configured to measure a first pressure at a first time and a second pressure at a second time. The microprocessor is configured to receive the first pressure and the second pressure from the pressure transducer, determine a pressure difference between the first pressure and the second pressure, and determine
a time difference between the first time and the second time. Successful situation of needle is determined from the pressure difference and the time difference, which may be converted into a pressure-time ‘slope’. A further (third) pressure at a later time point may also be measured to confirm success.
Published patent application US 2011/0301500 to Maguire et al. discloses an automated vessel puncture device using three-dimensional near infrared imaging and a robotically driven needle to providing simultaneous real-time diagnostic assays. It teaches that venipuncture is the process of obtaining a sample of venous blood for purposes of performing various tests. Samples are obtained manually from a vein or organ that is close to the surface of the skin by trained personnel, but there are problems inherent with these processes. This reference uses infrared imaging and a robotically driven needle to address the problem but does not use fluid pressure values to help indication the presence of vein or organ. Although pressure is mentioned, this refers to mechanical pressure resisting the movement of the mechanically driven needle to avert injury to the patient, not to fluid pressure in the needle.
It can be seen from the above that a novel system for guiding a needle to an anatomical target region which assists practitioners in discriminating between False-LOR and True-LOR would provide a contribution to the art.